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Mar 14, 2019
03/19

by
Alejandro Ferron

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Un grupo de científicos presenta una nueva técnica que permite controlar el magnetismo de un átomo de cobre aislado. Esta tecnología podría utilizar, en un futuro no muy lejano, núcleos atómicos para guardar y procesar información. Polarización nuclear de átomos aislados controlada eléctricamente es el título del trabajo, que fue realizado de manera colaborativa por físicos experimentales y teóricos de Estados Unidos, Corea, Argentina, Portugal, Suiza, Reino Unido y España.

Topics: magnetismo, átomo, núcleos atómicos, átomos aislados

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31

Sep 19, 2013
09/13

by
Alejandro Ferron; Daniel Dominguez

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Solid state devices for quantum bit computation (qubits) are not perfect isolated two-level systems, since additional higher energy levels always exist. One example is the Josephson flux qubit, which consists on a mesoscopic SQUID loop with three Josephson junctions operated at or near a magnetic flux of half quantum. We study intrinsic leakage effects, i.e., direct transitions from the allowed qubit states to higher excited states of the system during the application of pulses for quantum...

Source: http://arxiv.org/abs/0910.5640v2

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33

Sep 18, 2013
09/13

by
Alejandro Ferrón; Pablo Serra; Omar Osenda

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We present a way to manipulate an electron trapped in a layered quantum dot based on near-threshold properties of one-body potentials. We show that potentials with a simple global parameter allows the manipulation of the wave function changing its spatial extent. This phenomenon seems to be fairly general and could be implemented using current quantum-dot quantum wells technologies and materials if a proper layered quantum dot is designed. The layered quantum dot under consideration is similar...

Source: http://arxiv.org/abs/1201.0145v2

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35

Sep 21, 2013
09/13

by
Alejandro Ferrón; Pablo Serra; Omar Osenda

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In this work we present a model qubit whose basis states are eigenstates of a multi-layered quantum dot. We show that the proper design of the quantum dot results in qubit states that have excellent dynamical properties when a time-dependent driving is applied to it. In particular, it is shown that a simple sinusoidal driving is sufficient to obtain good quality Rabi oscillations between the qubit states. Moreover, the switching between states can be performed with very low leakage, even under...

Source: http://arxiv.org/abs/1301.2726v1

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37

Sep 23, 2013
09/13

by
Alejandro Ferron; Daniel Dominguez; Maria Jose Sanchez

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We distinguish different mechanisms for population inversion in flux qubits driven by dc+ac magnetic fields. We show that for driving amplitudes such that there are Landau-Zener-St\"uckelberg intereferences, it is possible to have population inversion solely mediated by the environmental bath at long driving times. We study the effect of the resonant frequency $\Omega_p$ of the measuring circuit, finding different regimes for the asymptotic population of the state of the flux qubit. By...

Source: http://arxiv.org/abs/1202.5445v2

2
2.0

Jun 28, 2018
06/18

by
Alejandro Ferron; Daniel Dominguez; Maria Jose Sanchez

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We study Landau-Zener-Stuckelberg (LZS) interferometry in multilevel systems coupled to an Ohmic quantum bath. We consider the case of superconducting flux qubits driven by a dc+ac magnetic fields, but our results can apply to other similar systems. We find a dynamic transition manifested by a symmetry change in the structure of the LZS interference pattern, plotted as a function of ac amplitude and dc detuning. The dynamic transition is from a LZS pattern with nearly symmetric multiphoton...

Topics: Quantum Physics, Superconductivity, Condensed Matter, Mesoscale and Nanoscale Physics

Source: http://arxiv.org/abs/1511.09400

2
2.0

Jun 29, 2018
06/18

by
Alejandro Ferrón; Daniel Domínguez; María José Sánchez

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We investigate flux qubits driven by a biharmonic magnetic signal, with a phase lag that acts as an effective time reversal broken parameter. The driving induced transition rate between the ground and the excited state of the flux qubit can be thought as an effective transmitance, profiting from a direct analogy between interference effects at avoided level crossings and scattering events in disordered electronic systems. For time scales prior to full relaxation but large compared to the...

Topics: Mesoscale and Nanoscale Physics, Quantum Physics, Condensed Matter

Source: http://arxiv.org/abs/1610.07502

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2.0

Jun 30, 2018
06/18

by
Alejandro Ferrón; Fernando Delgado; Joaquín Fernández-Rossier

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A method to calculate the effective spin Hamiltonian for a transition metal impurity in a non- magnetic insulating host is presented and applied to the paradigmatic case of Fe in MgO. In a first step we calculate the electronic structure employing standard density functional theory (DFT), based on generalized-gradient approximation (GGA), using plane waves as a basis set. The corresponding basis of atomic-like maximally localized Wannier functions is derived and used to represent the DFT...

Topics: Mesoscale and Nanoscale Physics, Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1412.7956

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Sep 23, 2013
09/13

by
Alejandro Ferrón; Daniel Domínguez; María José Sánchez

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The device for the Josephson flux qubit (DJFQ) can be considered as a solid state artificial atom with multiple energy levels. When a large amplitude harmonic excitation is applied to the system, transitions at the energy levels avoided crossings produce visible changes in the qubit population over many driven periods that are accompanied by a rich pattern of interference phenomena. We present a Floquet treatment of the periodically time-dependent Schr\"odinger equation of the strongly...

Source: http://arxiv.org/abs/1006.3505v2

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4.0

Jun 28, 2018
06/18

by
Alejandro Ferrón; Jose Luis Lado; Joaquín Fernández-Rossier

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We study the nature of spin excitations of individual transition metal atoms (Ti, V, Cr, Mn, Fe, Co and Ni) deposited on a Cu$_2$N/Cu(100) surface using both spin-polarized density functional theory (DFT) and exact diagonalization of an Anderson model derived from DFT. We use DFT to compare the structural, electronic and magnetic properties of different transition metal adatoms on the surface. We find that the average occupation of the transition metal d shell, main contributor to the magnetic...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1506.04941

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3.0

Jun 29, 2018
06/18

by
Diego S. Acosta Coden; Rodolfo H. Romero; Alejandro Ferrón; Sergio S. Gomez

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We study the efficiency of modulated laser pulses to produce efficient and fast charge localization transitions in a two-electron double quantum dot. We use a configuration interaction method to calculate the electronic structure of a quantum dot model within the effective mass approximation. The interaction with the electric field of the laser is considered within the dipole approximation and optimal control theory is applied to design high-fidelity ultrafast pulses in pristine samples. We...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1603.03718

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Sep 18, 2013
09/13

by
Diego S. Acosta Coden; Rodolfo H. Romero; Alejandro Ferrón; Sergio S. Gomez

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We present a detailed analysis of the electronic and optical properties of two-electron quantum dots with a two-dimensional Gaussian confinement potential. We study the effects of Coulomb impurities and the possibility of manipulate the entanglement of the electrons by controlling the confinement potential parameters. The degree of entanglement becomes highly modulated by both the location and charge screening of the impurity atom, resulting two regimes: one of low entanglement and other of...

Source: http://arxiv.org/abs/1209.1959v2